1. Field of Invention
The present invention relates to an organic electro-luminescence (EL) element, a method for manufacturing the same, and a display device. More specifically, the invention relates to the configuration of an organic EL element with excellent reliability.
2. Description of Related Art
In recent years, a display device with an organic EL element has been in the spotlight as a selfluminous type display device. It has been thought that the organic EL element itself may be used as, not only a display for representation, but also a frontlight (illumination device) for a nonluminous type display device, such as a reflected type liquid crystal panel. In the case of using an organic EL element as a display for representation, it may be so arranged that a metal electrode used as a cathode is formed on the substrate and users visually recognize through a transparent electrode used as an anode with a light emitting layer interposed between the electrodes. In this case, the cathode can be formed over the entire surface of the substrate without the need for patterning. In contrast, for example, in the case of using an organic EL element as a frontlight for a display device, cathodes each composed of a metal electrode cannot be formed over the entire surface of the substrate, so that cathode patterning is required in order to visually recognize the display.
FIG. 17 is a view showing an example of the basic configuration of a conventional organic EL element used as a frontlight for a display device. The organic EL element 103 is arranged to have a transparent electrode (anode) 117, a hole transport layer 122, a light emitting layer 118 of an organic EL material, and cathodes 121, which are stacked on a glass substrate 116 in order, and further a sealing layer 126 formed so as to cover the resultant substrate and a cover glass 127 formed on the sealing layer. The organic EL element emits light through recombination of holes and electrons in the light emitting layer 118, when holes and electrons are injected into the light emitting layer 118 from positive and negative electrodes.
In the organic EL element 103, in order to enhance an electron injection efficiency of electrons injected from the cathodes 121 into the light emitting layer 118, keep the stability of the cathodes, and ensure the reflectivity, as the cathodes 121 are used multilayered electrodes each composed of an alkaline-earth metal layer 119 of a material with a low work function such as calcium (Ca) and magnesium (Mg), and a metal layer 120 of a material with a higher work function and a high visible light reflectivity such as aluminum (Al) and silver (Ag).